Rotary fluid pump



y 1 3 R.-J. MCLEOD I Q ROTARY 'FLUHID PUMP,

Filed Dec 23, 1952 v I INVENTOR' Robert J. McLeqd ATTORNEY Patented May 12, 1936 Application December 23, 1932, Serial No. 648,678 In Great Britain September 30,

' z ciiaiia (01. 103-126).;53

This lnventibn relates .torotary pumps. of the type employing gear wheels as rotors. It is fre quentiy necessary-I for such pump to have a compactness and portability in ahandy form and-at Q 5 the sametime arrange for high rotational speeds and high volumetric efiiciency. Now, in employ-' ing gear wheels of the spur and helical type. cer-i tain well-known disadvantages arise. In the 3 formertype pulsation of :the'fluidis causedbythe action of a-t0oth .on,-the one wheel: entering the fluid fllled space between the. teeth on the .other.

taneous displacement of thisfluid;

This eifectis, particularly in high speed pumps, undesirable and results in" objectionable noise and T vibration. L

Y In order togovercomezthispulsation, one com men-expedient. whichghas been 1 adopted is to cut a channel atieach end in the side. or end.

plates ,or bearing housings and allow a slight leakage back to the suctionside, thus reducing the volumetric efflicie'ncy of the pump.

In the case of doublehelical, gears objection has always been raised on the groundthat the fluid would partiallyrunhback into the suction side unless the "spiral anglewas' small. a

.The well known quality of helical gear rotors that tooth engagement is such that all phases of tooth contact take place simultaneously enables a pump to be constructed whichis practically free from pulsation with its accompanying disadvantages. a V It is well known thatin order to preserve the quality of helical gears,'that all phases of tooth engagement take place simultaneously, that the width of the tooth face must have a certain minimum value depending on the number of teeth on a given rotor'and the spiral .angle. It has been stated that in known constructions an in- 40 crease in spiral angle is considered undesirable. It, therefore, remains that if the face width is varied, the number of teeth must be varied. If the gear rotors of a fluid pump are constructed with teeth of normal proportions, they are liable to have the serious disadvantagethat the face width is suchthat an open. passage is formed between the inlet and outlet sides of the pump.

If the'face width is reduced so that this passage is prevented, from the above state'r'nent it will; be seen that with teeth of normal proportions the number of teeth must' be increased if continuity of phase engagement is to be retained. Such increase,however, involves fresh difllculties both in manufacture and in the design of an eflicient pump.

a pitch diameter of the gear byjvr.

in order to avoid the difflculties causedby an increase in the number of teeth and of alteration'of'jthe spiral. angle when the face width reduced; according to the invention a fluid rotary pump of the kind referred to is provided' 'with" 5 double helical toothed rotors which arepro V vided with teeth, the addenda of whichare' in;

creased'in radial directionandare g'reater'than the value given by the reciprocal of the diame j tral' pitch and thededenda greater than. the i0 value 1.1 diyided by the diametral pitch, the a wheel and. effecting a. bulk.; .and almost instan rotors intermeshing in-nonnalmanner, that is according to Brown and Sharpe's standards-or nasesortoothensasemenmhe tom face width of" each;;double helicalftoothd. e. thetotal face a width or the rotor)" being "shortert han; the 'distance given bydne quarter "the product" of the A pump constructed accordi "g to the inven-" tion is capable of rotating at very high speeds, for example'3000 to"9qil0 revolutions jper-minute without pulsation.,f"' w", v

consequence'of "such highfspeeds, the 'volumetric capacity of the pump is high in proportion to its size, the dimensions of the teeth, of course,

forming a factor in the obtaining of'such volumetric efliciency.

The number of teeth always in engagement shall not be less than two and may be three.

The teeth may be designed to conform approximately to the following formula:

, cos PAXCP I Where C=center distance of wheel and pinion;

N 1average' number of teeth in continuous engagement. w I

Rp=blank radius of pinion. rp=base circleradius of pinion. Rw=blank radius of wheel.

. rw=base circleradius wheel. 7

PA=pressure angle. 1 45 CP=circular pitch. I Applying the aboveformula to a pair of pump rotors as actually used, wherein the values are as follows:-- a i To find number of pairs of teeth in continuous engagement Since wheel and pinion are identical, the formula becomes:

In the above example 30 degrees spiral angle and .5" face width are used. To obtain cover with standard teeth, the face width would have to be .7852".

In the accompanying drawing, which illustrates one construction of a pump embodying the invention- Fig. 1 is, a vertical section of the pump, partly in elevation.

Fig. 2 is a sectional plan.

Fig. 3 illustrates the contour of the teeth with the extended zone of engagement represented by the line X-Y. I

In Figs. 1 and 2 the driving and driven double helical toothed rotors a and b respectively are carried on or made solid with their spindles (11,

D1. The spindles are carried inbearings c, c,

preferably of the ball or roller type, but which may also be of the journal type. Each of the bearings is mounted in separate housings d, d, d, d which are made a tight push fit in the bores of the pump body It. On the lower ends, as shown,

of the bearing housings remote from the driving coupling g are fitted plates orsolid washers e, e. Adjusting screws 1, I provided with suitable lock nuts carried in the body It engage with the washers e, e and may be set to adjust the clearances of the pump rotors a, b to very flne limits in order to reduce leakages to a minimum.

The adjusting screws f, ,f are made hollow and fitted with grease nipples. A small hole In drilled. through the spindle b1 of the driven rotor b connects with an open passage it between the ends of the top bearings'and allows the top bearing of the driving rotor 12 to be-lubricated from the same point as the two bearings of the driven rotor b. The bottom bearing or the driving rotor a. is lubricated separately from the nipple attached to its own: adjusting screw. The body end plates and the safety valve are of usual construction.

The inlet side which is determined by the di-- rection of rotation may be at either side of the pump, the rotors entering mutual engagement at the delivery side.

1. A fluid, rotary pump comprising a casing, an inlet and an outlet therefor, toothed rotors, meshing one with the other, means for driving said rotors, the addenda of the teeth on the rotors being greater than the value given by the reciprocal of the diametral pitch, and the dedenda greater than the value 1.1 divided by the dimetral pitch, the rotors intermeshing in normal manner with simultaneous engagement of the teeth' in all phases of tooth engagement, the total face width of each double helical tooth (i'. e. the total face width of the rotor) being shorter than the distance given by one quarter the product of the pitch diameter of the gear by 1, whereby the teeth at the point of intermesh and around the peripheries of the rotors inhibit passage of fluid from outlet to inlet.

2. A fluid rotary pump as claimed in claim 1, comprising housings in said casing, bearings supported in said housings for carrying said rotors, screws supported in said casing and co-operating with said housings for adjusting the position of said housings in relation to said rotors.

ROBERT JAMES MCLEOD.

double helical 

